The present invention relates to a touch panel placed on a screen of display devices such as LCDs (liquid crystal displays), CRTs (cathode ray tubes), or the like with which position input is obtained by being depressed from above by a finger or pen in accordance with instructions on the seen-through screen.
Conventionally, as shown in FIG. 4, a transparent touch panel of a resistance film system is so constructed that a pair of an upper electrode sheet 101 and a lower electrode sheet 102 having transparent electrodes of ITO or the like on transparent films respectively are arranged opposite to each other via spacers 103 of an insulating substance between the electrodes, and a transparent hold plate 105 of a resin totally is bonded to a lower face of the lower electrode sheet 102 via a transparent adhesive layer 104 (referring to FIG. 5).
For the transparent films of the upper electrode sheet 101 and the lower electrode sheet 102, a polyethylene terephthalate-film of a thickness of 100-200 xcexcm superior in flexibility to pressing at the input time is used, which is generally biaxially stretched. For the transparent hold plate 105, a polycarbonate plate of a thickness of 0.5-3.0 mm with a superior rigidity for protecting a screen of an LCD or the like from pressing at the input time is used, which is generally unstretched.
The polyethylene terephthalate film used for the transparent film of the lower electrode sheet 102 and the polycarbonate plate used for the transparent hold plate 105 are different in thermal expansion coefficient, and moreover the former is stretched whereas the latter is unstretched. The transparent film of the lower electrode sheet 102 is bonded totally, that is, over the entire face to the transparent hold plate 105. As such, the transparent hold plate 105 changes differently in size between the side of the lower electrode sheet and the opposite side when the touch panel is exposed to a severe temperature environment or humidity environment. The touch panel sometimes warps to project upward at its central part (with reference to FIG. 5). This warp produces an air layer between the touch panel and the screen under the touch panel, whereby a sense of touch in operation is dulled because of an unnecessary deflection applied to the whole of the touch panel at the input time.
The warp could be forcibly corrected to make the touch panel flat in setting the touch panel on the screen of the LCD, CRT, or the like. This, however, leads to waving the transparent film of the upper electrode sheet 101 and worsening an appearance or look of the touch panel and a visibility of the screen. The waving of the transparent film of the upper electrode sheet 101 changes a gap between electrodes irregularly, consequently varying the sense of touch depending on spots of the touch panel. An insulation failure may also be brought about through mutual touch of the electrodes if the waving of a large size takes place.
An object of the present invention is therefore to provide a touch panel superior in flexibility for a pressing operation at the input time and rigidity for protecting a screen of a display device such as an LCD, CRT, or the like from the pressing operation, which hardly warps even exposed to a severe temperature environment or humidity environment, with solving the above-described issues.
In order to accomplish the above object, the present invention is so constructed as follows.
According to a first aspect of the present invention, there is provided a touch panel in which an upper electrode sheet having an upper transparent electrode formed on a transparent film of polyethylene terephthalate and a lower electrode sheet having a lower transparent electrode formed on a transparent film of polycarbonate are arranged opposite to each other via a plurality of spacers of an insulating substance between the upper and lower electrodes, while a transparent hold plate of a polycarbonate plate is bonded over an entire face to a lower face of the lower electrode sheet via a transparent adhesion layer.
According to a second aspect of the present invention, there is provided the touch panel according to the first aspect which uses a polycarbonate film of a thickness of 50-300 xcexcm for the transparent film of the lower electrode sheet.
According to a third aspect of the present invention, there is provided the touch panel according to the first or second aspect the transparent hold plate of which is a polycarbonate plate of a thickness of 0.5-3.0 mm having a rigidity for protecting a screen of a display apparatus from pressing at the input time.
According to a fourth aspect of the present invention, there is provided the touch panel according to any one of the first through third aspects in which the transparent adhesion layer is a transparent acrylic adhesive approximate in refractive index to the transparent film of the lower electrode sheet and the transparent hold plate.
According to a fifth aspect of the present invention, there is provided the touch panel in any one of the first through fourth aspects which uses a polycarbonate film of a thickness of 50-300 xcexcm for the film of the lower electrode sheet, with the transparent adhesion layer being adapted to keep an elastic modulus of 5xc3x97105-5xc3x97107 dynes/cm2 at ordinary temperatures.
According to a sixth aspect of the present invention, there is provided the touch panel according to any one of the first through fifth aspects which is arranged on a screen of a display apparatus to enable position input when pressed from above by a finger or pen in accordance with instructions on the seen-through screen.